Method for modifying fluoring resin film

ABSTRACT

A simple short-time method for modifying a fluorine resin film so that hydrophilicity is not likely to deteriorate over time. The method for modifying a fluorine resin film is characterized in that the surface of the fluorine resin film is provided with hydrophilicity by bringing the fluorine resin film into contact with a process gas, which contains gas containing fluorine atoms and at least one of gas containing oxygen atoms or inert gas.

This application is the U.S. National Phase under 35. U.S.C. § 371 ofInternational Application PCT/JP2009/061111, filed Jun. 18, 2009, whichclaims priority to Japanese Patent Application No. 2008-160889, filedJun. 19, 2008. The International Application was published under PCTArticle 21(2) in a language other than English.

TECHNICAL FIELD

The present invention relates to a method for modifying a fluorine resinfilm in order to give hydrophilicity to a surface of the fluorine resinfilm.

BACKGROUND ART

As aback sheet material for a solar battery, use is made of a fluorineresin film such as a polyvinyl fluoride (PVF) film, an aluminum foillaminate, a polyethylene terephthalate (PET) film subjected to aluminumvapor deposition or Si vapor deposition, or some other film in order toimprove the weather resistance and the gas barrier performance. In thisway, solar battery cells, which are weak in humidity, are protected fromwater vapor.

Of the back sheet materials, the fluorine resin film is excellent fromthe viewpoint of long-term endurance. Therefore, demands of the film asa back sheet material have been increasing. In general, however,material made of a fluorine resin having a C—F bond has problems thatthe material is small in surface energy and shows water repellency andoil repellency, so as to be low in adhesiveness.

Examples of a technique for improving the adhesiveness of such fluorineresin films include plasma discharge treatment, corona dischargetreatment, and flame treatment. In these surface-modifying techniques, ahydrophilic functional group (such as a —COOH group, —OH group, SO₃Hgroup, or SO₂F_(x) group) is introduced into any surface of the resin,thereby improving the adhesiveness thereof.

However, according to these treating methods, a large-scale apparatus isrequired, and costs for the production increase. Moreover, there remainsa problem that after the surface modification, the film deterioratesheavily with the passage of time, and the adhesive performance thereofcannot be kept over a long term.

Patent document 1 described below describes a surface-modifying methodof selecting, as a synthetic or natural polymeric material, a materialwhich has a specific gravity of 1.6 or less and does not contain anether bond, carbonate bond, amide bond or urethane bond at all, and thenbringing a mixed gas composed of fluorine gas and a single gascontaining an oxygen element into contact with the synthetic or naturalpolymeric material, thereby giving hydrophilicity thereto. Thispublication includes a disclosure that according to thesurface-modifying method, the contact angle of any surface of thesynthetic or natural polymeric material to water is made small by 10degrees or more.

However, this conventional technique cannot be applied to any fluorineresin having a specific gravity of about 1.6 to 2.2 for the followingreason: in synthetic polymeric or natural polymeric material having aspecific gravity more than 1.6, the crystal structure thereof is grownor developed; therefore, fluorine gas does not diffuse therein easily,so that a surface-modification function is not easily expressed.

PRIOR ART DOCUMENTS

Patent Document

Patent document 1: Japanese Patent No. 3585833

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In light of the problems, an object thereof is to provide a method formodifying, simply in a short time, a fluorine resin film so as not to bedeteriorated in hydrophilicity with the passage of time. Another objectthereof is to provide a back sheet for a solar battery which has afluorine resin film yielded by the modifying method.

Means for Solving the Problems

In order to solve the problems in the prior art, the inventors have madeinvestigations on a method for modifying a fluorine resin film, and aback sheet for a solar battery. As a result, the inventors have foundout that the objects can be attained by adopting structures describedbelow, and have then made the invention.

In order to achieve the above described object, the present inventionrelates to a method for modifying a fluorine resin film, wherein aprocess gas which contains a gas containing fluorine atoms and at leastone of a gas containing oxygen atoms or inert gas is brought intocontact with the fluorine resin film, thereby giving hydrophilicity to asurface of the fluorine resin film.

According to the method, a process gas which contains a gas containingfluorine atoms and at least one of a gas containing oxygen atoms orinert gas is brought into contact with a surface of a fluorine resinfilm, thereby making it possible to conduct hydrophilicity-impartingtreatment simply in a short time while costs for the production arerestrained. According to the method, in the fluorine resin filmsubjected to the hydrophilicity-imparting treatment, deterioration inthe hydrophilicity thereof with the passage of time can be alsodecreased.

It is preferable that the fluorine resin film comprisestetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA),polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF),polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylenecopolymer (ETCFE), or ethylene/tetrafluoroethylene copolymer (ETFE).

It is preferable that the fluorine resin film comprises an additivereactive with the process gas.

When the additive, which is reactive with the process gas, isincorporated into the fluorine resin film, the impartation ofhydrophilicity onto the surface of the fluorine resin film is promoted.This manner makes it possible to conduct the hydrophilicity-impartingtreatment more effectively.

It is preferable that the content by percentage of the additive rangesfrom 0.1 to 90% by weight of the whole of the fluorine resin film.

And in order to achieve the above described object, the presentinvention relates to a back sheet for a solar battery, which has astructure wherein the above described fluorine resin films are bonded toboth surfaces of a substrate film, respectively, through an adhesive.

Since hydrophilicity is imparted to the fluorine resin film, the film isexcellent in adhesion to an adhesive. It is therefore possible that thefluorine resin film is bonded to each surface of a substrate film andthe resultant lamination is used as a back sheet for a solar battery.About the hydrophilicity imparted by the treatment, the performance canbe maintained over a long term; thus, the film is also excellent fromthe viewpoint of process-management, so that the reliability of theproduct is improved.

Advantageous Effects

The invention has the above-mentioned means, thereby producingadvantageous effects as described in the following:

According to the invention, a process gas which contains a gascontaining fluorine atoms and at least one of a gas containing oxygenatoms or inert gas is brought into contact with a surface of a fluorineresin film, thereby making it possible to conducthydrophilicity-imparting treatment simply in a short time while costsfor the production are restrained. Thus, the production efficiency isimproved. Moreover, the fluorine resin film yielded by the method can bepreferably used in, for example, a back sheet for a solar battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 The figure is a schematic view illustrating an example of areactor used for hydrophilicity-imparting treatment of a fluorine resinfilm according to an embodiment of the invention.

FIG. 2 The figure is a schematic sectional view which schematicallyillustrates a back sheet, for a solar battery, that has the fluorineresin film.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The method for modifying a fluorine resin film according to the presentembodiment is a method of bringing a process gas which contains a gascontaining fluorine atoms and at least one of a gas containing oxygenatoms or inert gas into contact with a fluorine resin film, which isrelatively low in critical surface tension and does not get wet easily,thereby making the film hydrophilic.

It is preferred to use a fluorine resin film the critical surfacetension of which is 18 mN/m or more, preferably 20 mN/m or more beforethe hydrophilicity-imparting treatment. If the critical surface tensionbefore the treatment is less than 18 mN/m, there is caused aninconvenience that hydrophilicity cannot be sufficiently given thereto.

It is also preferred that the fluorine resin film is made hydrophilic toset the critical surface tension of a surface or any surface thereof to25 mN/m or more, preferably 30 mN/m or more, more preferably 35 mN/m ormore. If the critical surface tension is less than 25 mN/m, the film isnot sufficiently made hydrophilic so that the adhesion thereof to anadhesive is unfavorably declined.

The value of the critical surface tension is calculated out as follows:use is made of a mixed solvent of ethylene glycol monoethyl ether andformamide which has an already-known surface tension (γ) (28 to 58 mN/m)and a mixed solvent of formamide and methylene blue which has analready-known surface tension (γ) (60 to 70 mN/m) to measure the contactangle (θ) of the fluorine resin film surface to each of the solvents;next, values of cos θ (Y axis) versus γ (X axis) are plotted; and theextrapolative value of γLV giving 1 as a value of the solid/liquidcontact angle cos θ is calculated, whereby the critical surface tensionvalue is obtained. The larger the numerical value of the criticalsurface tension is, the higher the wettability is; and the smaller thenumerical value of the critical surface tension is, the lower thewettability is

The fluorine resin film may have a monolayered structure or a laminatedstructure wherein at least two films are laminated onto each other. Thethickness of the fluorine resin film (when the film has a laminatedstructure, the thickness is the total thickness of the individuallayers) is not particularly limited, and ranges preferably from, forexample, 10 to 100 μm. The two-dimensional shape of the fluorine resinfilm is not particularly limited, and may be appropriately set inaccordance with request.

The constituting material of the fluorine resin film is not particularlylimited as far as the material has, in the molecular structure thereof,at least one of a nitrogen-containing group, a silicon-containing group,an oxygen-containing group, a phosphorus-containing group, asulfur-containing group, a hydrocarbon group, and a halogen-containinggroup. Examples of the nitrogen-containing group include amide and aminogroups. Examples of the silicon-containing group include trialkylsilyl,silyl ether, and —Si(CH₃)₂O— groups. Examples of the oxygen-containinggroup include ester, carbonate, and ether groups. Examples of thephosphorus-containing group include a phosphoryl choline group. Examplesof the sulfur-containing group include sulfo, and sulfonyl groups.Examples of the hydrocarbon group include methyl, methylene and phenylgroups. Examples of the halogen-containing group include a —CHX— group,a —CHX₂ group, a —CX₂— group, and a —CX₃ group wherein X(s) is/are atleast one selected from the group consisting of F, Cl, Br and I atoms.Specific examples thereof include tetrafluoroethylene/perfluoroalkylvinyl ether copolymer (PFA), polyvinylidene fluoride (PVDF), polyvinylfluoride (PVF), polychlorotrifluoroethylene (PCTFE),ethylene/chlorotrifluoroethylene copolymer (ETCFE), andethylene/tetrafluoroethylene copolymer (ETFE). These may be used aloneor in combination of two or more thereof.

When the fluorine resin film has a laminated structure composed of atleast two films, the constituting material of the film on the frontsurface side may be identical with or different from that of the film onthe rear surface side. When the constituting materials of the two filmsare made different from each other, the film of the front surface can bemade different in the degree of hydrophilicity from that of the rearsurface in accordance with the combination of the materials even whenthe films are subjected to the hydrophilicity-imparting treatment underthe same conditions.

It is preferred to add, into the fluorine resin film, an additivereactive with the process gas. This makes it possible that for thehydrophilicity-imparting treatment with the process gas, thehydrophilicity-impartation can be further promoted.

When the fluorine resin film has a laminated structure composed of atleast two films, the composition ratio of the additive in the film onthe front surface side may be identical with or different from that ofthe additive in the film on the rear surface side. When the compositionratios of the additive are made different from each other, the film onthe front surface side can be made different in critical surface tensionvalue from the film on the rear surface side even when the films aresubjected to the hydrophilicity-imparting treatment under the sameconditions. In short, in the film wherein the addition amount of theadditive is larger, the film is made higher in hydrophilicity even whenthe films are treated under the same conditions.

The additive is classified into organic additives and inorganicadditives. The organic additives are preferably resin components thatare different from the polymeric compounds given as examples of theconstituting material of the fluorine resin film and each have, in themolecular structure thereof, a functional group reactive with theprocess gas. When such a resin component is contained therein, thefluorine-atom-containing gas reacts with the reactive functional groupso that the fluorinating treatment is promoted. In this way, thehydrophilicity is further improved.

Examples of the functional group reactive with the process gas include anitrogen-containing group, a silicon-containing group, anoxygen-containing group, a phosphorus-containing group, asulfur-containing group, a hydrocarbon group, and a halogen-containinggroup. Examples of the nitrogen-containing group include amide and aminogroups. Examples of the silicon-containing group include trialkylsilyl,silyl ether, and —Si(CH₃)₂O— groups. Examples of the oxygen-containinggroup include ester, carbonate, and ether groups. Examples of thephosphorus-containing group include a phosphoryl choline group. Examplesof the sulfur-containing group include sulfo, and sulfonyl groups.Examples of the hydrocarbon group include methyl, methylene and phenylgroups. Examples of the halogen-containing group include a —CHX— group,a —CHX₂ group, a —CX₂— group, and —CX₃ group wherein X(s) is/are atleast one selected from the group consisting of F, Cl, Br and I atoms.

More specifically, the resin components are, for example, polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polybutylene terephthalate (PBT),polycyclohexanedimethanol terephthalate (PCT), polycarbonate (PC), andpolyolefins. These resin components may be used alone or in combinationof two or more thereof.

The inorganic additives are not particularly limited, and examplesthereof include white pigments such as titanium oxide and calciumcarbonate, and black pigments such as carbon black. These inorganicadditives may be used alone or in combination of two or more thereof.Any of the organic additives may be used together with any of theinorganic additives.

The addition amount of the additive is not particularly limited, and ispreferably from 0.1 to 90% by weight of the whole of the fluorine resinfilm, more preferably from 0.1 to 80% by weight thereof. If the additionamount is less than 0.1% by weight, for example, the film may not obtaina sufficient hydrophilicity even when the film is subjected to thehydrophilicity-imparting treatment. By contrast, if the addition amountis more than 90% by weight, there is caused an inconvenience thatperformances of the fluorine resin itself cannot be kept.

The process gas is not particularly limited as far as the gas is a gaswhich contains a gas containing fluorine atoms and at least one of a gascontaining oxygen atoms or inert gas. The fluorine-atom-containing gasis not particularly limited, and examples thereof include hydrogenfluoride (HF), fluorine (F₂), trifluorochlorine (ClF₃),tetrafluorosulfur (SF₄), trifluoroboron (BF₃), and trifluoronitrogen(NF₃). These gases may be used alone or in combination of two or morethereof.

The method of the invention for modifying a fluorine resin film can beperformed in such a range that the fluorine-atom-containing gasconcentration is from 0.001 to 99% by volume of the whole of the processgas. However, if the fluorine-atom-containing gas concentration islarge, a damage may be given to the fluorine resin film, which is aproduct to be treated. It is therefore preferred that the gasconcentration is low. Specifically, the concentration is, for example,from 0.001 to 50% by volume, more preferably from 0.001 to 10% byvolume.

The oxygen-atom-containing gas is not particularly limited, and examplesthereof include oxygen gas (O₂), sulfur dioxide gas (SO₂), and carbonylfluoride (COF₂). These gases may be used alone or in combination of twoor more thereof.

The method of the invention for modifying a fluorine resin film can beperformed in such a range that the oxygen-atom-containing gasconcentration is from 0.001 to 99% by volume of the whole of the processgas. However, the oxygen-atom-containing gas can produce an advantageouseffect thereof sufficiently even in a small amount. It is thereforepreferred from the viewpoint of treatment costs also that the gasconcentration is low. Specifically, the concentration is, for example,from 0.01 to 50% by volume, more preferably from 0.01 to 20% by volume.

An inert gas, such as dry air, nitrogen, argon, helium, neon, krypton orxenon, may be blended with the process gas in order to dilute theprocess gas.

The method of the invention for modifying a fluorine resin film can beperformed by use of, for example, a reactor illustrated in FIG. 1 .Prepared is first a reactor 4 for subjecting any fluorine resin film tohydrophilicity-imparting treatment, and a fluorine resin film 5 is putin the reactor 4. The reactor 4 is not particularly limited, and may be,for example, a reactor made of stainless steel, aluminum or nickel.

Next, when the pressure in the reactor 4 is reduced, a valve of a vacuumline 7 is opened to degas the reactor into a vacuum. After the pressurereaches a predetermined pressure (for example, 10 Pa), the valve of thevacuum line 7 is closed.

As needed, next, the following valves are appropriately opened: valvesof a first supply line 1 through which a fluorine-atom-containing gas issupplied; a second supply line 2 through which an oxygen-atom-containinggas is supplied; and a third supply line 3 through which an inert gas issupplied. A process gas which is thus adjusted into predeterminedconcentrations is introduced into the reactor 4.

In this way, the process gas is brought into contact with the fluorineresin film 5 to subject the film 5 to a hydrophilicity-impartingtreatment. The critical surface tension of the fluorine resin film 5after the hydrophilicity-imparting treatment can be controlled bysetting the concentration of the process gas, the treating period, thetreating temperature, and the gas flow rates as needed. However, whenthe surface area of the fluorine resin film 5 is large, it is necessaryto use treating conditions and a reactor corresponding to the sizethereof. The reaction may be conducted while the process gas iscontinuously supplied under normal pressure, increased pressure orreduced pressure. Alternatively, the reaction may be conducted in astate sealed at normal pressure, increased pressure or reduced pressure.

The concentration of the fluorine-atom-containing gas in the process gascan be adjusted through the gas amount supplied from each of the firstsupply line 1 to the third supply line 3.

The treating period for the hydrophilicity-imparting treatment is notparticularly limited. The reaction between the fluorine resin and theprocess gas is explosively generated at the initial stage of thereaction; thus, by the treatment for a relatively short period, theadvantageous effects of the hydrophilicity-impartation are obtained.Specifically, the period ranges, for example, from 1 second to 600minutes, preferably from 1 second to 100 minutes, more preferably from 1second to 30 minutes. If the treating period is less than 1 second, asufficient hydrophilicity may not be given to the fluorine resin film 5.

The treating temperature for the hydrophilicity-imparting treatment isnot particularly limited. Considering the heat resistant temperature ofthe fluorine resin film 5 (when the additive is added thereto, the heatresistant temperature thereof is considered), the treating temperatureis preferably from −50 to 150° C., more preferably from 0 to 100° C. Ifthe treating temperature is lower than −50° C., a sufficienthydrophilicity may not be given to the fluorine resin film 5. Bycontrast, if the treating temperature is higher than 150° C., thefluorine resin film is thermally deformed so that the yield may bedeclined.

The gas flow rate of the process gas flowing in the reactor 4 is notparticularly limited. When the gas flow rate is large, the reaction maybe explosively caused; thus, at the initial stage of the reaction, it isimportant to set the concentration of the fluorinated gas and the flowrate appropriately. In other words, in accordance with the progress ofthe reaction, the concentration and the flow rate may be appropriatelymade large or small. The gas flow rate may be appropriately set inaccordance with the size of the reactor 4 and the shape of the fluorineresin film 5.

After the end of the hydrophilicity-imparting treatment, the valve ofthe third supply line 3 is opened to introduce an inert gas, therebysubstituting the inert gas, at a predetermined flow rate, for theprocess gas in the reactor 4. At this time, a valve of an exhaust line 6is also opened. Thereafter, the valves of the third supply line 3 andthe exhaust line 6 are closed and further the valve of the vacuum line 7is opened so as to degas the reactor 4 into a vacuum until the inside ofthe reactor 4 turns into a predetermined pressure (for example, 10 Pa).

Next, the valve of the vacuum line 7 is closed and the valve of thethird supply line 3 is opened to introduce the inert gas into thereactor so as to turn into the atmospheric pressure. When the inside ofthe reactor 4 turns into the atmospheric pressure, the valve of theexhaust line 6 is opened and then the fluorine resin film 5 subjected tothe hydrophilicity-imparting treatment is taken out.

The fluorine resin film taken out from the reactor 4, which has beensubjected to the hydrophilicity-imparting treatment, may be washed witha washing liquid such as water or an alcohol. This manner makes itpossible to remove unreacted F₂, which is adsorbed on the fluorine resinfilm surface, or HF, which is generated by the reaction, so that ahydrophilic surface excellent in stability can be formed.

The fluorine resin film yielded by a hydrophilicity-imparting treatmentas described above can be favorably applied to, for example, a backsheet for a solar battery. When the sheet is used as a back sheet for asolar battery, the film may be in a form as illustrated in FIG. 2 .Specifically, fluorine resin films 8 according to the invention arebonded to both surfaces of a substrate film 9, respectively, through anadhesive. At this time, the fluorine resin films 8 of the invention haveundergone the hydrophilicity-imparting treatment, as described above;thus, the adhesion thereof to the adhesive is good so that the films canbe prevented from being peeled on the basis of being deteriorated withthe passage of time. The thus-produced laminated film has a gas barrierperformance against water vapor, oxygen gas and some other gas. Thus, aback sheet for a solar battery that is excellent in reliability can beproduced.

The adhesive is not particularly limited, and may be, for example, aurethane adhesive or an epoxy adhesive. A pressure-sensitive adhesive(sticky agent) may be used. The pressure-sensitive adhesive is notparticularly limited, and may be, for example, an acrylic, rubbery orurethane sticky agent.

EXAMPLES

Hereinafter, preferred examples of this invention will be illustrativelydescribed in detail. However, materials, blend amounts and so on thatwill be described in the examples are not intended to limit the scope ofthis invention into only the described materials and so on as far as norestrictive description thereabout is included. Thus, the materials andso on are mere descriptive examples.

Example 1

As illustrated in FIG. 1 , a PVDF film (trade name: NAFLON, manufacturedby Nichias Corp.; thickness: 2 mm) was first introduced, as a fluorineresin film 5, into the reactor 4. Next, the valve of the vacuum line 7was opened to reduce the pressure in the reactor 4 down to 10 Pa orless.

Next, the valve of the vacuum line 7 was closed, and then the valve ofthe first supply line 1, for the supply of fluorine-atom-containing gas,and that of the second supply line 2, for the supply ofoxygen-atom-containing gas, were simultaneously opened to introduce aprocess gas into the reactor 4 until the pressure thereof turned to theatmospheric pressure, the process gas being adjusted as follows: theratio (by volume) of fluorine gas/oxygen gas/nitrogen gas therein was5/95/0, and the total flow rate being 1.0 L/min. Furthermore, the valvesof the first supply line 1 and the second supply line 2 weresimultaneously closed to make the inside of the reactor into an airtightstate. The reactor was then kept as it was for 5 minutes. Thetemperature of the inside of the reactor 4 was kept at 30° C. After alapse of a predetermined period, the valves of the third supply line 3,for the supply of inert gas, and the exhaust line 6 were opened tosubstitute nitrogen gas, at a flow rate of 10 L/min, for the mixed gasof fluorine gas, oxygen gas and nitrogen gas in the reactor 4.Thereafter, the valves of the third supply line 3 and the exhaust line 6were closed and the valve of the vacuum line 7 was opened to reduce thepressure in the reactor into 10 Pa or less.

Next, the valve of the vacuum line 7 was closed and the valve of thethird supply line 3 was opened to introduce nitrogen gas at a flow rateof 1.0 L/min into the reactor 4 until the pressure thereof turned to theatmospheric pressure. After the inside of the reactor 4 turned to theatmospheric pressure, the valve of the exhaust line 6 was opened to takeout the PVDF film subjected to the hydrophilicity-imparting treatment.

The taken-out PVDF film was washed with UPW (ultra pure water) of roomtemperature, which was being stirred, for 1 hour. After the washing, UPWon the surfaces was blown by effect of nitrogen gas, and then the filmwas dried at room temperature under a reduced pressure until thepressure turned to 10 Pa or less. A device, Drop Master 300,manufactured by Kyowa Interface Science Co., Ltd. was used to measurethe contact angle (θ) of the dried PVDF film. The used measuring liquidwas a surface energy measuring agent (surface tension γ: 25 to 70 mN/m)manufactured by Arcotest Co. Values of the cos θ (Y axis) versus γ (Xaxis) were plotted, and the extrapolative value of γLV giving 1 as avalue of the solid/liquid contact angle cos θ was calculated, wherebythe values were obtained. The results are shown in Table 1 describedbelow.

Example 2

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that a PVF film (trade name: TEDLAR,manufactured by DuPont) was used as the fluorine resin film. Thereafter,values of the critical surface tension were calculated out.

Example 3

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that a PFA film (trade name: NAFLON,manufactured by Nichias Corp.) was used as the fluorine resin film.Thereafter, values of the critical surface tension were calculated out.

Example 4

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that a PCTFE film (trade name:YODOFLON, manufactured by Yodogawa Hu-Tech Co., Ltd.) was used as thefluorine resin film. Thereafter, values of the critical surface tensionwere calculated out.

Example 4

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that an ETFE film (trade name:YODOFLON, manufactured by Yodogawa Hu-Tech Co., Ltd.) was used as thefluorine resin film. Thereafter, values of the critical surface tensionwere calculated out.

Example 6

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that the process gas was changed to agas wherein the ratio (by volume) of fluorine gas/sulfur dioxidegas/nitrogen gas was 5/95/0. Thereafter, values of the critical surfacetension were calculated out.

Example 7

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that the process gas was changed to agas wherein the ratio (by volume) of fluorine gas/carbonyl fluoridegas/nitrogen gas was 5/95/0. Thereafter, values of the critical surfacetension were calculated out.

Example 8

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that the process gas was changed to agas wherein the ratio (by volume) of fluorine gas/nitrogen gas was0.001/99.999. Thereafter, values of the critical surface tension werecalculated out. The supply of the process gas into the reactor 4 wasperformed by closing the valve of the vacuum line 7, opening the valvesof the first supply line 1, for the supply of fluorine-atom-containinggas, and the third supply line 3, for the supply of nitrogen gas,simultaneously, and further closing the second supply line 2, for thesupply of oxygen-atom-containing gas.

Example 9

In the present example, the same hydrophilicity-imparting treatment asin Example 8 was conducted except that a PVF film (trade name: TEDLAR,manufactured by DuPont) was used as the fluorine resin film. Thereafter,values of the critical surface tension were calculated out.

Example 10

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that the treating period was set to0.5 minute and the temperature of the inside of the reactor 4 waschanged to 100° C. Thereafter, values of the critical surface tensionwere calculated out.

Example 11

In the present example, the same hydrophilicity-imparting treatment asin Example 10 was conducted except that a PVF film (trade name: TEDLAR,manufactured by DuPont) was used as the fluorine resin film. Thereafter,values of the critical surface tension were calculated out.

Example 12

In the present example, the same hydrophilicity-imparting treatment asin Example 1 was conducted except that the process gas was changed to agas wherein the ratio (by volume) of fluorine gas/oxygen gas/nitrogengas was 0.5/20/79.5, the treating period was set to 1 minute and thetemperature of the inside of the reactor 4 was changed to 50° C.Thereafter, values of the critical surface tension were calculated out.The supply of the process gas into the reactor 4 was performed byclosing the valve of the vacuum line 7, and opening the valves of thefirst supply line 1, for the supply of fluorine-atom-containing gas, thesecond supply line 2, for the supply of oxygen gas, and the third supplyline 3, for the supply of nitrogen gas, simultaneously.

Example 13

In the present example, the same hydrophilicity-imparting treatment asin Example 12 was conducted except that a PVF film (trade name: TEDLAR,manufactured by DuPont) was used as the fluorine resin film. Thereafter,values of the critical surface tension were calculated out.

Example 14

In the present example, the same hydrophilicity-imparting treatment asin Example 2 was conducted except that a PVF film to which PMMA wasadded in an amount of 30% by weight of the whole of the film was used asthe fluorine resin film. Thereafter, values of the critical surfacetension were calculated out.

Example 15

In the present example, a PVDF film to which PMMA (polymethylmethacrylate) was added in an amount of 30% by weight of the whole ofthe film was used as the fluorine resin film. The treating period wasset to 5 minutes, and the temperature of the inside of the reactor 4 waschanged to 30° C. Except the changes, the same hydrophilicity-impartingtreatment as in Example 12 was conducted. Thereafter, values of thecritical surface tension were calculated out.

Example 16

In the present example, the same hydrophilicity-imparting treatment asin Example 15 was conducted except that a PVDF film to which PMMA wasadded in an amount of 90% by weight of the whole of the film was used asthe fluorine resin film. Thereafter, values of the critical surfacetension were calculated out.

TABLE 1 Treating conditions Critical surface tension (mN/m)Concentration Temperature Period Before the After the After one SpeciesAdditive Gas species (% by volume) (° C.) (min) treatment treatmentmonth Example 1 PVDF None F₂/O₂/N₂ 5/95/0 30 5 25 31 Not changed Example2 PVF None F₂/O₂/N₂ 5/95/0 29 38 Not changed Example 3 PFA None F₂/O₂/N₂5/95/0 18.5 20 Not changed Example 4 PCTFE None F₂/O₂/N₂ 5/95/0 31 35Not changed Example 5 ETFE None F₂/O₂/N₂ 5/95/0 22 30 Not changedExample 6 PVDF None F₂/SO₂/N₂ 5/95/0 25 32 Not changed Example 7 PVDFNone F₂/COF₂/N₂ 5/95/0 25 31 Not changed Example 8 PVDF None F₂/O₂/N₂0.001/0/99.999 25 30 Not changed Example 9 PVF None F₂/O₂/N₂0.001/0/99.999 29 31 Not changed Example 10 PVDF None F₂/O₂/N₂ 5/95/0100 0.5 25 34 Not changed Example 11 PVF None F₂/O₂/N₂ 5/95/0 29 40 Notchanged Example 12 PVDF None F₂/O₂/N₂ 0.5/20/79.5 50 1 25 31 Not changedExample 13 PVF None F₂/O₂/N₂ 0.5/20/79.5 29 38 Not changed Example 14PVF PMMA F₂/O₂/N₂ 5/95/0 30 5 27 40 Not 30 wt % changed Example 15 PVDFPMMA F₂/O₂/N₂ 0.5/20/79.5 27 36 Not 30 wt % changed Example 16 PVDF PMMAF₂/O₂/N₂ 0.5/20/79.5 27 40 Not 930 wt % changed

REFERENCE NUMERALS

-   -   1 first supply line    -   2 second supply line    -   3 third supply line    -   4 reactor    -   5 fluorine resin film    -   6 exhaust line    -   7 vacuum line    -   8 fluorine resin film    -   9 substrate film

The invention claimed is:
 1. A method for producing a backsheet for asolar battery comprising, preliminarily preparing a process gas in anon-plasma state by mixing a gas consisting of fluorine atoms at aconcentration of 0.001 to 99% by volume and an inert gas consisting ofnitrogen, argon, helium, neon, krypton, or xenon in the absence of afluorine resin film; and imparting hydrophilicity to a surface of thefluorine resin film only by carrying out a reaction resulting from atreatment consisting of contacting the process gas in the non-plasmastate with the fluorine resin film for a period of 1 second to 5minutes, said fluorine resin film consisting essentially of a fluorineresin film other than ethylene/tetrafluoroethylene copolymer (ETFE),thereby producing a hydrophilized fluorine resin film, washing thehydrophilized fluorine resin film subjected to thehydrophilicity-imparting treatment with a washing liquid in air underatmospheric pressure thereby removing an unreacted gas consisting offluorine atoms, which is adsorbed on the surface of the hydrophilizedfluorine resin film, and HF, which is generated by contacting theprocess gas with the fluorine resin, and drying the hydrophilizedfluorine resin film subjected to the washing, and thereafter bonding thedried hydrophilized fluorine resin film to both surfaces of a substratefilm through an adhesive, thereby producing the back sheet for a solarbattery, wherein the fluorine resin film has a specific gravity greaterthan 1.6 and 2.2 or less, thereby giving hydrophilicity to the surfaceof the fluorine resin film that has a critical surface tension of 18mN/m or more, wherein the surface of the hydrophilized fluorine resinfilm has a critical surface tension that is greater than the criticalsurface tension of the fluorine resin film and that is 30 mN/m or more,and wherein the fluorine resin film comprises 0.1 to 90% by weight of anorganic additive having a functional group reactive with the processgas, wherein the functional group is selected from the group consistingof amide, amino, trialkylsilyl, silyl ether, —Si(CH₃)₂O—, ester,carbonate, ether, phosphorylcholine, sulfo, sulfonyl, methyl, methylene,phenyl, —CHX—, —CHX₂, —CX₂, and —CX₃, wherein X is at least one of F,Cl, Br, or I.
 2. The method for producing a backsheet for a solarbattery according to claim 1, wherein the fluorine resin film comprisestetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA),polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF),polychlorotrifluoroethylene (PCTFE), or ethylene/chlorotrifluoroethylenecopolymer (ETCFE).
 3. The method for producing a backsheet for a solarbattery according to claim 1, wherein the fluorine resin film ispolyvinylidene fluoride (PVDF) or polyvinyl fluoride (PVF), and theorganic additive is polymethyl methacrylate (PMMA).